Plating apparatus

ABSTRACT

An apparatus for plating workpieces by electrolytic treatment in several steps comprises means (2) to hold and rotate the workpiece (5), a plurality of electrodes, at least one of which being adapted, in each step, to be located at the workpiece by means of a holder (10), and means to supply, in each step, a certain electrolyte to the region of the rotating workpiece and the non-rotating electrode. A plurality of electrode holders (10) with associated electrodes are arranged on a common carrier (11), which is adjustably movable relative to the rotatable workpiece (5) to selectively locate an optional electrode holder with associated electrode(s) intended for the desired treatment step in an operative position relative to the rotatable workpiece. The carrier (11) is preferably rotatable.

TECHNICAL FIELD

The invention relates to an apparatus for plating workpieces byelectrolytic treatment in a plurality of steps, comprising means to holdand rotate the workpiece, a plurality of electrodes, at least one ofwhich being adapted, in each step, to be located at the workpiece bymeans of an electrode holder, and means to supply, in each step, acertain electrolyte to the region of the rotating workpiece and thenon-rotating electrode, which during the treatment is connected to onepole of a source of direct current, the other pole of which is connectedto the workpiece.

BACKGROUND ART

By means of this known apparatus, so called brush plating may be carriedout, which is an electrolytic method for metallizing without need ofimmersing the workpiece in an electrolytic bath. In each treatment step,one or more electrodes, normally anodes, which typically are made ofgraphite and wound with an absorbing material, such as cotton orpolypropylene wool or the like, are located adjacent the rotatingworkpiece, the absorbing material being in contact with the workpiecewhile the electrode proper may be located at a distance of e.g. 0.5 mmsor less from the workpiece. The electrolyte is supplied to the area ofthe electrode and the workpiece and metals ions are deposited from theelectrolyte on the surface of the workpiece adjacent to the electrode.In order to obtain a complete plating treatment, several steps arerequired. A first step may be degreasing, a second activation orpickling, a third deposition of a binding metal layer and a fourthdeposition of the main metal layer. Each of said steps is carried outwith a specific electrolyte and one or more specific electrodes.

Although it is possible with said apparatus to obtain high qualityplating, there are nevertheless disadvantages as to the efficiencythereof. In practice, an electrode holder is provided to which a firstelectrode must be mounted for carrying out the first treatment step,i.e. degreasing. In addition, a hose or the like must be applied to theelectrode to supply the degreasing electrolyte to the electrode. Whenthe degreasing step is terminated, the electrode must be released fromthe holder and another electrode, e.g. an electrode for a picklingelectrolyte, be mounted on the holder and in addition, anotherelectrolyte container must be taken to the vicinity of the holder andconnected to the pickling electrode by a hose. In an analogous manner,the treatment proceeds until the plating is completed by deposition ofthe main metal layer. In practice, such a plating operation may comprisefour or more treatment steps and it is evident that the treatment as awhole is very laborious.

DISCLOSURE OF INVENTION

The object of the invention is to eliminate the disadvantage describedabove and enable a plating treatment as rapid and efficient as possible.In particular, the invention aims at enabling fully automatic plating ofworkpieces in long series.

According to the invention this object is obtained in that a pluralityof electrode holders with associated electrodes are arranged on a commoncarrier, which is adjustably movable relative to said holding means andthe rotatable workpiece to selectively locate an optional electrodeholder with associated electrode(s) intended for the desired treatmentstep in an operative position relative to the rotatable workpiece. Inthis way, it is possible to rapidly and efficiently carry out severalsuccessive treatment steps by moving the carrier relative to theworkpiece so that the holders in question with associated electrodessequentially are brought into operative position relative to theworkpiece without necessitating individual manipulating and mounting ofelectrodes.

It is preferred that the carrier is rotatable.

BRIEF DESCRIPTION OF DRAWINGS

With reference to the appended drawings, a more specific disclosure ofan embodiment of the invention follows hereinbelow.

In the drawings

FIG. 1 is a perspective view of the apparatus, certain parts beingomitted for clarity;

FIG. 2 is a top view of a portion of FIG. 1;

FIG. 3 is a composite cross section of a carrier of the apparatus, theupper part in FIG. 3 being a section along line IIIa--IIIa in FIG. 1 andthe lower portion of FIG. 3 being a section along line IIIb--IIIb inFIG. 1; and

FIG. 4 is an enlarged detail view illustrating an electrolytic treatmentstep on the interior surface of a hollow cylinder.

BEST MODE FOR CARRYING OUT THE INVENTION

The apparatus illustrated in the drawings comprises a housing 1containing suitable drive equipment to rotate a chuck 2. Workpieces tobe plated by the apparatus may be clamped in the chuck. In order tosupport longer workpieces (see e.g. FIG. 2, wherein the workpiece is along shaft 5) a tail stock 3 is provided having an adjustable dog 4. Thetail stock 3 is displacable along a guide beam 6, which preferably islocated above, suitably obliquely above the axis of rotation of chuck 2.The guide beam 6 is at one end connected to housing 1 and at the otherend carried by two struts 7.

In order to carry out plating of a workpiece by electrolytic treatmentin several steps, a plurality of electrodes 8, 9 (see FIG. 3) isrequired, at least one of which being adapted, in each step, to belocated at the workpiece 5 by a holder generally denoted 10. A pluralityof holders 10 with associated electrodes are provided on a commoncarrier 11, which is movable relative to the workpiece to enable anoptional holder with associated electrode to be located in operativeposition relative to the workpiece.

For clarity, only one holder 10 is partially shown in FIG. 1. In FIG. 2,a holder is completely illustrated with full lines while several otherholders 10 are partially indicated with dashed lines. In the embodiment,the number of holders is 6 and it should in the following disclosure bekept in mind that all holders in practice are identical, In FIG. 3 aholder 10 is illustrated in its entirety while an additional holder ispartially indicated.

The carrier 11 is in its entirety rotatable about a stationary shaft 12which is surrounded by a sleeve portion 13 of the carrier. The carrieris hexagonal in plan view and adapted to carry six electrolytecontainers 14 appearing in FIG. 1 but not illustrated in FIG. 3. Theelectrolyte containers 14 are as many as the electrode holders 10. Thecarrier 11 has an upper plate 15, a bottom plate 16 and an intermediateplate 17 located rather close to the upper plate 15. These three platesare interconnected by six vertical rods 18 arranged in the corners ofcarrier 11. The electrolyte containers 14 have a triangular form in planview so that they, when they are inserted into carrier 11, form aconfiguration corresponding to the hexagonal shape of the carrier. Thecarrier 11 has no side walls so that each electrolyte container 14 isinsertable into the carrier between two adjacent rods 18. Thus, theelectrolyte containers are easily removable from and insertable intocarrier 11 if another electrolyte would be required. Each electrolytecontainer has means, such as a pump and necessary hoses, to supplyelectrolyte to the region of the electrode(s) 8,9, which are carried bythe holder 10 located above the electrolyte container 14 in question.

As appears by FIG. 3, the sleeve 13 of the carrier is connected to thebottom plate 16. To enable rotation of carrier 11 about shaft 12, aschematically indicated transmission gear 19 is provided thereon, saidgear meshing with another diagrammatically indicated gear 20 adapted tobe driven by a motor 21 via a suitable transmission 22. The motor 21 andtransmission 22 are connected to plate 17 and accompany carrier 11 inits rotation while gear 20 is rolling on the circumference of gear 19.Motor 21 is reversible to enable rotation of the carrier in eitherdirection of rotation.

The carrier 11 is displacable perpendicular to the axis of rotation ofthe workpiece. This is obtained in that shaft 12 is rigidly connected toa plate 23 movable along guides 24 extending transversely to the axis ofrotation of chuck 2. The guides 24 may e.g. have an U-shaped crosssection while angle pieces 25 may be attached to plate 23. Suitableslide bearing elements 26 are provided between guides 24 on one hand andplate 23 and angle pieces 25 respectively on the other hand. To displacethe carrier, plate 23 is rigidly connected to a nut 27 meshing with ascrew 28 (FIG. 1) rotatable by a motor 29 via a transmission 30.

Furthermore, carrier 11 is displacable along the axis of rotation ofchuck 2. The guides 24 are connected to two sleeves or slides 31, on oneof which motor 29 and transmission 30 are attached. Said two slides 31each runs on a guide 32, which are located spaced from each other andparallel to the axis of rotation of chuck 2. Guides 32 have thecharacter of box girders and are at one end connected to housing 1 andat their other end interconnected by a cross piece 33 also connected tostruts 7. A screw (not illustrated) is provided in each box girder 32.Each box girder has a longitudinal slot 33 and each slide has aprojection (not illustrated) provided with a nut, said projectionprotruding down into the slot 33 so that the nut meshes with the screw.The screws in the box girders 32 are in a suitable manner driven insynchronism so that slides 31 are displaced completely parallel to avoidseizure. To eliminate entrance of pollutions into the interior of thebox girders and between slides 31 and the box girders, bellows 34 arepreferably provided, only one of which is indicated in FIG. 1. Thebellow illustrated therein is attached at one end to the slide 31 and atits other end to housing 1 and surrounds partially the box girder 32. Inanalogy therewith, the other portions of the box girders 32 not coveredby the slides 31 are surrounded by additional bellow sections. The samemay also be valid in connection with guides 24 and screw 28. The bellowsare particularly important since the apparatus operates withelectrolytes which could be disastrous to the displacement component. Itis evident that also the screws in box girders 32 are reversibly driven.As appears by FIGS. 1-3, the holders 10 of the carrier 11 aredistributed about the circumference of the carrier and located ingenerally the same plane. A bracket 35 is connected to the upper plate15 of carrier 11 and has six vertical holes 36'. Each holder 10 (FIG. 3)comprises a first piston-cylinder mechanism 36 to move the associatedelectrodes 8, 9 to and fro in a direction perpendicular to the axis ofrotation of carrier 11. The piston-cylinder mechanism has two ears 37engaging about a portion of bracket 35. A screw 38 projects through ears37 and one of the holes 36' in bracket 35 so that piston-cylindermechanism 36 is connected to bracket 35 but pivotable in a planeperpendicular to the axis of rotation of carrier 11. To secure thepiston-cylinder mechanism in a desired pivotable position, an anglepiece 39 is connected to the cylinder thereof, one flange 40 of saidpiece comprising a downwardly projecting screw 41 extending through aslot 42 in plate 15. A locking nut 42' enables securing of thepiston-cylinder mechanism in a desired pivotal position. The piston rod43 of piston-cylinder mechanism 36 is attached to a carrier plate 44 towhich also the cylinders of two other piston-cylinder mechanisms 45, 46are attached. Two holder members 47 and 48 are pivotably connected toears 49 attached to carrier plate 44 so that holder members 47, 48 arepivotable about generally horizontal pivotal shafts 50. The holdingmembers 47, 48 have each a projecting plate 51, to which the piston rodof the respective piston-cylinder mechanisms 45, 46 is connected in apivotal manner (not illustrated) about shafts parallel to shafts 50.Each of the holding members 47, 48 have a sloping surface 52, on whichthe electrode 8, 9 is attached. In practice, the electrodes 8, 9 areusually anodes and this denomination will for simplicity be usedhereinbelow. Each anode 8, 9 has in the embodiment a partially annularconfiguration to be able to partially surround a workpiece in the formof shaft 5. Each anode 8, 9 is in a way not illustrated adjustablyconnected to the holding member 47 and 48 respectively so that the anodemay be moved and secured in a desired position on sloping surface 52.

The anodes 8, 9 are also readily removable from holding members 47, 48to enable exchange of the anodes when a workpiece having another form isto be plated. The supply of electrolyte to anodes 8, 9 and shaft 5occurs via hoses communicating with associated electrolyte containers14. In practice, the electrolyte supply may occur via holes 53 in anodes8, 9, said hoses being connected to said holes 53. Holding members 47,48 are suitably manufactured from metal but each includes, in order toavoid disturbance of the plating, an electric interruption 54 obtainedby an isolating piece of plastics material connecting the two spacedportions of each holding member. To collect excessive electrolyte, thelower holding member 48 carries a collecting vessel 55, which isprovided with an outlet (not illustrated) communicating via a hose withthe associated electrolyte container to return excessive electrolytethereto. It is evident that the length of holding members 47, 48perpendicularly to the plane of the drawing (FIG. 3) may be optional independence upon the length of workpiece 5 and the same applies foranodes 8, 9. Piston-cylinder mechanisms 36, 45 and 46 have in a knownmanner adjustment means (not illustrated) to enable accurate regulationof the stroke of the piston-cylinder mechanism. Furthermore, it is to beunderstood that piston-cylinder mechanism 36 in a known manner isprovided with guide means to prevent piston rod 43 from rotating aboutits own axis.

In relation to FIG. 3, it is to be noted that anodes 8, 9 need notsurround the entire circumference of workpiece 5. Anodes 8, 9 must,however, extend along the workpiece for the length thereof to be plated.In FIG. 2 it is illustrated that the holding members (only 47 isappearing) have an extent along workpiece 5, a shaft, which isconsiderably less than the length of the shaft. In this case also anodes8, 9 have an equally great or smaller extent as or than the holdingmembers and it is evident that electrolytic treatment and platingrespectively only is obtained along the length of the workpiece being incontact or close to the anodes.

From the above, it appears that six different electrolytic treatmentsteps may be carried out with the apparatus according to the invention.These different treatment steps are carried out by different anodeholders 10 and associated electrolyte containers 14. To simplify thefollowing disclosure, carrier 11 is in FIG. 2 by dashed lines dividedinto six triangular parts having a size corresponding to eachelectrolyte container 14. Each of said triangular parts represents anelectrolytic treatment step and the different parts are designated withthe letters A-F. In practice, the treatment step A may constitutedegreasing by means of a degreasing electrolyte in the associatedelectrolyte container. The treatment steps B, C and D enable activationtreatments, such as pickling, and the associated electrolyte containerscontain different activation electrolytes. The treatment step E mayserve to apply on the workpiece a primer or binder layer of a metalproviding the best adhesion of the material of which the workpiece ismanufactured. Thus, there is in the associated electrolyte container asuitable metal electrolyte. Finally, the treatment step F may serve toapply on the workpiece the main metal layer and in the associatedelectrolyte container there is a suitable metal electrolyte for thispurpose. The last mentioned electrolyte may be selected to obtain e.g. agood wear resistance, corrosion protection or other desirablecharacteristics.

The apparatus according to the invention may e.g. be used to repaircylindrical or conical surfaces on tools and machine parts when they aresubject to e.g. tolerance errors, wear, scores, corrosion or impactmarks. It is often possible to plate directly to desired tolerancewithout subsequent machining but in case of irregular wear, subsequentmachining in the form of turning, grinding, milling or polishing of theplating is normally required.

The apparatus according to the invention is used as follows. Referenceis made to the case according to FIGS. 2-3 in which a shaft 5 is to beplated. If the entire envelope surface of shaft 5 is to be plated, theanodes 8, 9 must, as pointed out previously, have a length correspondingto the length of shaft 5 and this is valid for the anodes on all holders10 to be used in the plating operation. In a typical plating operatione.g. five treatment steps (say A, B, D, E and F) may be required. Aparticular advantage with the apparatus according to the invention isthat it makes it possible to automatically plate large series of uniformworkpieces, which e.g. may have been manufactured to under-size. In sucha fully automatic operation the apparatus is adapted to be controlledvia a computer having predetermined treatment programs or sequences. Inorder to carry out plating of a series of shafts automatically, theactual treatment step must first be adjusted, unless advanced automaticsensing eliminates the need for manual adjustment. The manualadjustment, is, however, carried out in such a way that after havingprovided holding members 47 and 48 of the holders 10 to be used withsuitable anodes 8, 9 adapted to the shaft, the stroke of thepiston-cylinder mechanisms 36, 45 and 46 is adjusted so that anodes 8, 9are located, when the piston rods of the piston-cylinder mechanisms areextended, in a correct position relative to a shaft 5 clamped in chuck2. Before this adjustment of the strokes of the piston-cylindermechanisms is carried out, the position of carrier 11 along guides 24and 32 must have been adjusted and secured. When now the necessaryadjustment operations have been carried out, an automatic platingoperation may be initiated by operating the mentioned computer controlequipment. With the chosen treatment sequence, carrier 11 is initiallyrotated to the position according to FIG. 2 so that treatment step A maybe carried out. The shaft 5 clamped in chuck 2 is rotated andpiston-cylinder mechanism 36 expands and pushes the holding members 47,48 towards shaft 5. When the piston rod of piston-cylinder mechanism 36has reached the extreme position, piston-cylinder mechanisms 45, 46 areautomatically activated so as to pivot holding members 47, 48 from theinactive position indicated in FIG. 3 with dashed lines towards aposition closely adjacent shaft 5. Thereafter, a degreasing electrolyteis pumped from electrolyte container 14 in step A to anodes 8, 9 and isintroduced through holes 53 into contact with shaft 5. When thisdegreasing operation is terminated, holding members 47, 48 are pivotedaway by piston-cylinder mechanisms 45, 46, whereupon piston-cylindermechanism 36 retracts the holding member. Carrier 11 is then rotated soas to locate treatment step B opposite shaft 5 and a treatment step withan activation electrolyte is carried out in analogy with the degreasingoperation. In continued analogy with the degreasing operation, treatmentis then carried out with step C and an additional activationelectrolyte, step E involving deposition of a binder layer on shaft 5from a metal electrolyte and finally step F involving the finalmetallization with the main metal layer. During treatment by steps E andF the thickness of the deposited metal layer may be sensed by ameasuring device 56 diagrammatically indicated in FIG. 3 and being of aknown kind using optical or electroinductive measuring of the thicknessof the plating layer. Measuring device 56 may be adapted toautomatically terminate plating steps E and F when required layerthickness is reached. Measuring device 56 may be connected to a sleeve57 movable along beam 6.

As has been described above, a large number of uniform workpieces may berapidly and efficiently plated with the apparatus according to theinvention. Obviously, also shorter series of workpieces or individualworkpieces may be plated more rapidly and efficiently as has hithertobeen the case.

Since carrier 11 is not only rotatable but also displacable in twodirections perpendicular to each other, a great flexibility is obtainedand workpieces with markedly different shapes may be plated. Electrolytecontainers 14 may easily be exchanged for readjustment between differenttypes of plating operations and this is also due for anodes 8, 9 andtheir holding members 47, 48.

In FIG. 4 it is, as an example, illustrated how the internal surface ofa hollow cylindrical workpiece 5 is subjected to electrolytic treatment.In this case, piston-cylinder mechanism 46 of holding member 48 isswitched off so that it continuously is in the retracted position. Theholding member 47 on the other hand is illustrated with its associatedanode applied on the internal surface of cylinder 5. The anode 8 must ofcourse in this case protrude sidewardly relative to holding member 47.

The invention is of course in no way limited to the embodiment describedabove. Thus, carrier 11 may comprise more as well as fewer (e.g. two)than six holders 10 and electrolyte containers 14. Carrier 11 must notnecessarily be rotatable but may instead comprise a plurality of holdersdisposed side by side, which holders may be brought into alignment witha workpiece by straightly linear displacement of the carrier. Finally,manual displacement means are conceivable instead of piston-cylindermechanisms 36, 45 and 46.

I claim:
 1. An apparatus for plating workpieces by electrolytic treatment in a plurality of steps, comprising,means to hold and rotate the workpiece, a plurality of electrodes, at least one of which being adapted in each step to be located at the workpiece by means of an electrode holder, and means to supply, in each step, a certain electrolyte to the region of the rotating workpiece and the non-rotating electrode, which during the treatment is connected to one pole of a source of direct current, the other pole of which is connected to the workpiece, characterized in that a plurality of said electrode holders with associated ones of said electrodes are arranged on a common carrier, which is adjustably movable relative to said holding means and the rotatable workpiece to selectively locate an optional electrode holder with associated electrode(s) intended for the desired treatment step in an operative position relative to the rotatable workpiece, said holder and electrode(s) being adapted to remain on the carrier during the treatment step, and in that said carrier is provided with electrolyte containers in a number equal to the number of said electrode holders, each container being associated with means to supply electrolyte to the region of one of said electrode holders.
 2. Apparatus according to claim 1, characterized by said carrier being rotatable about an axis perpendicular to the axis of rotation of the workpiece.
 3. Apparatus according to claim 1, characterized in that said carrier is movable along the axis of rotation of the workpiece.
 4. Apparatus according to any one of claims 1, 2 or 3, characterized in that said carrier is movable at an angle to the axis of rotation of the workpiece.
 5. Apparatus according to claim 2, characterized in that said holders of said carrier are distributed about the circumference of said carrier and located generally in a common plane perpendicular to the axis of rotation of said carrier.
 6. Apparatus according to claim 1, characterized in that each of said holders is adapted to move its associated electrode toward and away from the workpiece.
 7. Apparatus according to claim 6, characterized in that each of said holders comprises at least one first operating means to move said electrode associated with said holder to an initial position rather close to the workpiece and at least one second operating means to move said electrode from the initial position to an operative position closely adjacent the workpiece.
 8. Apparatus according to claim 7, characterized in that said first operating means defines a linear path of movement, while said second operating means actuates said electrode about a pivotal axis perpendicular to said path.
 9. Apparatus according to any one of claims 1, 2 or 3, characterized by means for securing said electrode to its holder in an adjustable and removable manner. 